1. Field of the Invention
The present invention relates to a method for efficiently producing L-amino acids such as L-glutamic acid, L-glutamine, L-proline, L-arginine, L-leucine, and L-cysteine by fermentation.
2. Brief Description of the Related Art
L-amino acids are typically produced by various fermentation methods using L-amino acid-producing coryneform bacteria, including those belonging to the genus Brevibacterium, Corynebacterium, Microbacterium, or mutant strains thereof (Amino Acid Fermentation, Japan Scientific Societies Press, p. 195-215, 1986). Other bacterial strains have been used to produce L-amino acids by fermentation, and examples include microorganisms belonging to the genus Bacillus, Streptomyces, or Penicillium (U.S. Pat. No. 3,220,929), bacteria belonging to the genus Pseudomonas, Arthrobacter, Serratia, or Candida (U.S. Pat. No. 3,563,857), bacteria belonging to the genus Bacillus, Pseudomonas, Serratia, or Aerobacter aerogenes (currently, Enterobacter aerogenes) (JP 32-9393 B), mutant strains of Escherichia coli (U.S. Pat. No. 5,378,616). Furthermore, methods for producing an L-amino acids using bacteria belonging to the genus Klebsiella, Erwinia, Pantotea, or Enterobacter (EP 955368 A, EP 952221 B, and EP 999282 A) have also been disclosed.
Various methods to increase the L-amino acid-producing ability of bacteria by enhancing activities of L-amino acid biosynthetic enzymes using recombinant DNA techniques have also been disclosed. For example, it has been reported that introducing a gene encoding citrate synthase derived from Escherichia coli or Corynebacterium glutamicum into a bacterium belonging to the genus Corynebacterium or Brevibacterium is effective to enhance the L-amino acid-producing ability of the bacterium (JP 07-121228 B). In addition, it has been reported that introducing a citrate synthase gene derived from a coryneform bacterium into an enterobacterium belonging to the genus Enterobacter, Klebsiella, Serratia, Erwinia, or Escherichia is effective to enhance L-glutamic acid-producing ability (EP 999282 A).
Phosphotransacetylase is an enzyme which is involved in acetic acid metabolism. In Escherichia coli, this enzyme plays a role in the reaction which produces acetyl phosphate from acetyl-CoA and phosphate, which is part of the primary pathway for producing acetic acid. Furthermore, it is known that in Corynebacterium glutamicum, phosphotransacetylase activity increases upon production of acetyl-CoA by assimilating acetic acid, and the activity is negatively regulated by the transcription factor RamB (Microbiology 1999 503-513, Journal of Bacteriology 2004 vol. 186, No. 9 p 2798-2809).
Examples of known methods of fermentative production of a useful material using a bacterium in which phosphotransacetylase activity is enhanced include production of poly-β-hydroxyalkanoate copolymer (U.S. Pat. No. 5,891,686 and U.S. Pat. No. 5,569,595), and production of ethanol (WO 2003/078643). Furthermore, an enzymatic method of producing a sulfur-containing L-amino acid using phosphotransacetylase has been disclosed (JP 09-009982 A). However, enhancing phosphotransacetylase activity in the breeding of L-amino acid-producing bacteria has not been reported, and the relationship between phosphotransacetylase activity and L-amino acid productivity has not been elucidated.